[RFC,v2,0/2] Rewrite parts of rkvdec driver and the VP9 codec library in Rust

Hi Mauro, Hans,

While working on v1 for this patchset, I realized that we can go further by
converting the error-prone sections of our codec drivers to Rust. This also
does not need any bindings in order to work.

As yet another proof-of-concept, I have converted parts of the rkvdec driver.
Refer to instructions in v1 to test this.

Notice how:

1) many problematic memcpy's go away, these become a simple assignment in Rust.

2) it can interop seamlessly with the code in rkvdec-vp9.c that was already
converted in v1 of this series.

3) it can use the Rust version of `seg_feat_enabled` directly in vp9.rs, while
also using the C APIs from the v4l2-vp9-rs library in rkvdec-vp9.c

4) more modern things become available for the programmer, like iterators and
their methods without a performance penalty.

I want to propose the following:

Let's merge a non-RFC version of this series and gate it behind some kconfigs
so that we can switch between the C and Rust implementations. Users get the C
version by default, while we continuously test the Rust components on a CI for
a few months. This will hopefully be enough time until the next Media Summit.

My aim is to eventually deprecate the C parts once we're confident that the
Rust code is stable enough. I will keep my own tree, and send PRs to the media
tree if a rebase or fix is needed.

I believe this will not be disruptive nor require any extra work from anyone
but me.

-- Daniel


Again, applies on top of:

commit d9c1fae3e5b225f2e45e0bca519f9a2967cd1062
Author: Alice Ryhl <aliceryhl@google.com>
Date:   Fri Feb 9 11:18:22 2024 +0000

    rust: file: add abstraction for `poll_table`

For those looking for a branch instead: https://gitlab.collabora.com/dwlsalmeida/for-upstream/-/tree/vp9-rs-rkvdec?ref_type=heads

Daniel Almeida (2):
  v4l2-core: rewrite the VP9 library in Rust
  media: rkvdec: rewrite parts of the driver in Rust

 drivers/media/platform/verisilicon/Kconfig    |    2 +-
 .../platform/verisilicon/hantro_g2_vp9_dec.c  |   38 +-
 .../media/platform/verisilicon/hantro_hw.h    |    8 +-
 drivers/media/v4l2-core/Kconfig               |    5 +
 drivers/staging/media/rkvdec/Kconfig          |    3 +-
 drivers/staging/media/rkvdec/Makefile         |    2 +-
 drivers/staging/media/rkvdec/cbindgen.toml    |   36 +
 drivers/staging/media/rkvdec/common.rs        |   19 +
 drivers/staging/media/rkvdec/regs.rs          |  237 ++
 drivers/staging/media/rkvdec/rkvdec-vp9.c     |  607 +----
 drivers/staging/media/rkvdec/rkvdec_rs.h      |  125 +
 drivers/staging/media/rkvdec/rkvdec_rs.rs     |   14 +
 drivers/staging/media/rkvdec/vp9.rs           |  636 +++++
 include/media/v4l2-vp9-rs.h                   |   99 +
 rust/bindings/bindings_helper.h               |    1 +
 rust/helpers.c                                |    7 +
 rust/kernel/lib.rs                            |    2 +
 rust/kernel/media.rs                          |    5 +
 rust/kernel/media/v4l2_core.rs                |    6 +
 rust/kernel/media/v4l2_core/cbindgen.toml     |   26 +
 rust/kernel/media/v4l2_core/vp9.rs            | 2053 +++++++++++++++++
 21 files changed, 3415 insertions(+), 516 deletions(-)
 create mode 100644 drivers/staging/media/rkvdec/cbindgen.toml
 create mode 100644 drivers/staging/media/rkvdec/common.rs
 create mode 100644 drivers/staging/media/rkvdec/regs.rs
 create mode 100644 drivers/staging/media/rkvdec/rkvdec_rs.h
 create mode 100644 drivers/staging/media/rkvdec/rkvdec_rs.rs
 create mode 100644 drivers/staging/media/rkvdec/vp9.rs
 create mode 100644 include/media/v4l2-vp9-rs.h
 create mode 100644 rust/kernel/media.rs
 create mode 100644 rust/kernel/media/v4l2_core.rs
 create mode 100644 rust/kernel/media/v4l2_core/cbindgen.toml
 create mode 100644 rust/kernel/media/v4l2_core/vp9.rs